SOLDERLESS WRAPPED CONNECTIONS — PART II 



583 



1.0 



0.9 



I 0.7 



lU 0.5 



I- 



(0 



0.4 



o 



O 0.1 

 a 



10" 



10" 



2 5 2 



1 10 



TIME IN YEARS 



5 2 5 2 5 



102 103 10" 



Fig. 22 — Aging at room temperature and at 135°F plotted as ratio of angle to 

 initial angle as a function of time. 



ture controlled air conditioned room and these agree well with the cal- 

 culated values. 135°F is in general the maximum temperature that 

 wrapped solderless connections will be subjected to. For cases of very high 

 temperature it is planned to use copper covered soft iron wires for the 

 wrapping wires since, as shown by Equation (17), iron has a much higher 

 activation energy than copper and can be expected to maintain its hoop 

 stress for forty years even under an ambient temperature of 200°C. 



The question arises as to whether the hoop stress of a small part of 

 the initial value, that has been shown to continue for a long time by 

 the data of Fig. 21, is sufficient to maintain a good contact. This ques- 

 tion may be important if aluminum is to be used as a wrapping wire 

 since with an activation energy of only 34.5 kilocalories, 0.5 of the hoop 

 stress will be maintained for forty years only for temperatures lower 

 than 100°F. The problem then is whether corrosion can occur between 

 the wrapping wire and the inside terminal when the relaxable com- 

 ponent of hoop stress has been relaxed. A very sensitive test for this 

 question is obtained by winding aluminum wire on an aluminum terminal 

 since if any break occurs in the contact between the wire and the termi- 

 nal, oxidation of the aluminum surface takes place very rapidly and 

 should affect the resistance of the solderless connection. Accordingly, a 

 number of aluminum-aluminum solderless connections were wound up 

 and their resistances were measured. They were then put in an oven 

 and heated to a temperature of 200°C for twelve hours, which was suffi- 



